Dynamical Adjustment of the Trade Wind Inversion Layer

Abstract

In schematic north–south cross sections the trade inversion layer is often depicted as sloping upward as air flows toward the intertropical convergence zone. This conceptual view is consistent with purely thermodynamic boundary-layer models, which predict a deeper boundary layer with increasing sea surface temperature and decreasing large-scale subsidence. The slopes implied by such thermodynamic models and incorporated into schematic diagrams are approximately 2000 m/1000 km. In contrast, observational studies of the inversion structure over the Atlantic and Pacific Oceans reveal a less dramatic slope, on the order of 300 m/1000 km. To address this inconsistency, the authors adopt a somewhat different view of the trade inversion layer. In particular, rather than regarding it as a purely thermodynamic structure, it is regarded as a dynamical structure. By formulating a generalization of the Rossby adjustment problem, the authors investigate the dynamical adjustments of a trade wind inversion layer of variable strength and depth. From the solution of the adjustment problem, there emerges the notion that the subtropics control the inversion structure in the Tropics; that is, the subtropical inversion height is dynamically extended into the Tropics in such a way that there is little variation in the depth of the boundary layer.